A vehicle grille is typically located at a front end of a vehicle, and can be configured to provide an opening through with intake air is received from outside of the vehicle, such as a grille opening or bumper opening. Such intake air may then be directed to an engine compartment of the vehicle to assist the vehicle's cooling system in cooling the engine, transmission, and other such components of the engine compartment. Such air flow via the grille may add aerodynamic drag when the vehicle is in motion. Accordingly, grilles may include grille shutters to block such air flow, thus reducing aerodynamic drag and improving fuel economy. Closed grill shutters may also provide a faster powertrain warm-up which may improve fuel economy since there is less friction, and may improve the performance of the passenger compartment heater. However, closed grille shutters also reduce the air flow through the radiator and other components for cooling purposes. As a result, engine temperatures such as engine coolant temperature (ECT) may increase. Thus, grille shutter operation may include increasing or decreasing the opening of the grille shutters based on engine cooling demands and vehicle driving conditions.
One example approach for adjusting grille shutters to increase fuel economy is shown by Kerns et al. in U.S. Pat. No. 8,311,708. Therein, vehicle grille shutters are adjusted in response to engine temperature and a non-driven vehicle condition. For example, when engine temperature is above a threshold temperature or the vehicle is decelerating, the grille shutters may be opened.
However, gear lash in the grille shutter system may result in differences between a commanded position of the grille shutters and the actual resulting position of the grill shutters. For example, a motor may adjust the grille shutters through a series of gears. However, the gears may include an amount of lash resulting in reduced accuracy of grille shutter positioning. A single map or relationship between desired grille shutter position and commanded grille shutter position may be used to adjust the grille shutters to a position close to the desired position. However, this relationship may change based on the direction of travel of the grille shutters (e.g., opening or closing), thereby resulting in decreased grille shutter position control.
In one example, the issues described above may be addressed by a method for adjusting a motor coupled to grille shutters based on a direction of motion of the grille shutters, a desired opening of the grille shutters, and vehicle speed. In this way, a position error between a commanded grille shutter position and the resulting grille shutter position may be reduced, thereby increasing vehicle fuel economy while providing adequate cooling to the engine.
As one example, unique opening and closing maps (or relationships) may be stored within a memory of a controller of the engine. The unique opening and closing maps may include a commanded percentage opening or closing (depending on the chosen map) corresponding to a desired percentage opening or closing at a current vehicle speed. In one example, the map may be stored at a look-up table within the memory of the controller. The opening or closing map for determining the commanded grille shutter position may be determined based on a desired motor position relative to a current or previously desired motor position. For example, if a difference between the desired motor position (based on desired grille shutter position) and the current (e.g., actual) motor position is greater than one motor increment, the controller may use the opening map to determine the commanded grille shutter position. However, if instead a difference between the current motor position and the desired motor position is greater than one motor increment, the controller may use the closing map to determine the commanded grille shutter position. In this way, determining the commanded grille shutter position based on the desired grille shutter position, as well as vehicle speed and the direction of motion of the grille shutters, may result in an actual grille shutter position closer to the commanded grille shutter position. As a result, fuel economy may be increased along with accuracy of engine temperature control.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.